Wow51900319 Error Message

This is frustrating, I just logged back onto the game after years of not playing. Now I am getting this (WOW51900319) Error after putting in the correct information and I still am not able to log in to play this game. I can log into other games with no issues using Battle.net but now WOW. WTF?! Need some clear cut answers and guidance on what I need to do to mitigate this error message.